Supramolecular Assembly-Improved Triplet–Triplet Annihilation Upconversion in Aqueous Solution

Article abstract of DOI:10.1002/chem.201804001

Water-soluble 9,10-diphenylanthracene-modified γ-cyclodextrin derivatives A1 and A2, in which the γ-cyclodextrin unit serves as a molecular host for a binding sensitizer, and the 9,10-diphenylanthracene moiety plays a role as an emitter/annihilator, were synthesized to investigate the supramolecular triplet–triplet annihilation (TTA) upconversion in aqueous solution. Both A1 and A2 readily aggregate and form nanoscale assemblies in water as a combined result of host–guest complexation and π–π stacking among the 9,10-diphenylanthracenes. The aggregation behavior of the supramolecular emitters was fully characterized by using a diversity of methods, including dynamic light scattering (DLS), SEM, NMR, fluorescence, and circular dichroism studies. Fluorescence spectroscopic analysis reveals that the emitters have high fluorescence quantum yields in water (82 and 90 % for A1 and A2, respectively), thus demonstrating that aggregation does not quench the fluorescence. By using a coordinated ruthenium sensitizer, a high TTA upconversion quantum yield of up to 6.9 % was observed for this supramolecular TTA system, which is significantly higher than the value (<0.5 %) obtained with nonassembled emitters in organic solvent and in contrast to the fact that TTA upconversion emission in aqueous solution is usually low or negligible. We ascribe the strong TTA upconversion emission in the present supramolecular assembly system to an efficient TTA process, which is facilitated along the stacked emitters by triplet energy migration and improved triplet–triplet energy transfer through host–guest complexation.

Full text of DOI:10.1002/chem.201804001

A Journal of
Accepted Article
Title: Supramolecular Assembly-Improved Triplet-Triplet Annihilation
Upconversion in Aqueous Solution
Authors: Wei Xu, Wenting Liang, Wanhua Wu, Chunying Fan, Min
Rao, Dan Su, Zhihui Zhong, and Cheng Yang
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To be cited as: Chem. Eur. J. 10.1002/chem.201804001
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Supramolecular Assembly-Improved Triplet-Triplet Annihilation
Upconversion in Aqueous Solution
Wei Xu, [a] Wenting Liang, [b] Wanhua Wu, *[a] Chunying Fan, [a] Min Rao, [a] Dan Su, [a] Zhihui Zhong, [a]
and Cheng Yang*[a]
triplet sensitizer/energy donor and energy acceptor/annihilator
deliver the excited energy through diffusion in the solution to
complete the upconversion process.[2,3] As illustrated in Figure 1,
the photosensitizer absorbs the low-energy photons and
transfers the energy to the acceptor through triplet-triplet energy
transfer (TTET) after the population of the triplet state by
Abstract: Water-soluble 9, 10-diphenylanthracene-modified -
cyclodextrin derivatives A1 and A2, in which the -cyclodextrin
serves as the molecular host for binding sensitizer, and the 9, 10-
intersystem crossing (ISC), to afford the acceptor of triplet
diphenylanthracene moiety plays a role of emitter/annihilator, were
excited state. The subsequent TTA taking place between two
synthesized for investigating the supramolecular triplet-triplet
excited triplets eventually created one excited singlet, the
annihilation (TTA) upconversion in aqueous solution. Both A1 and
radiative transition from which gives the high-energy photos,
which is the so-called upconverted delayed fluorescence. During
A2 readily aggregate and form nanoscale assemblies in water as a
combined result of the host-guest complexation and - stacking
the recent decade, numerous efforts have been made to
among the 9, 10-diphenylanthracenes. The aggregation behavior of
optimize the photophysical properties of the sensitizers and
the supramolecular emitters was fully characterized by a diversity of
reasonable TTA-UC quantum yield have been achieved with the
methods, including DLS, SEM, NMR, fluorescence and circular
excitation power as low as the solar irradiance in nonviscous
dichroism spectroscopic studies. Fluorescence spectroscopic
organic solvents.[3] However, TTA-UC is rarely observed in
investigation reveals that the emitters have high fluorescence
aqueous solution due to poor solubility of organic sensitizers and
quantum yield in water (82% for A1 and 90% for A2), demonstrating
emitters, and the aggregation of these organic components often
that aggregation does not quench the fluorescence. By using a
significantly change their photophysical and molecular motional
coordinated ruthenium sensitizer, high TTA upconversion quantum
properties.[4] Both the TTET and TTA processes obey the Dexter
yield up to 6.9% was observed in this supramolecular TTA system,
energy transfer mechanism,[5] which demands intimate contact
which is significantly higher than the value (<0.5%) obtained with the
between energy donor and acceptor. In non-viscous organic
non-assembled emitters in organic solvent and in contrast to the fact
solvents, the TTA-UC components can freely diffuse to
that TTA upconversion emission in aqueous solution is usually low
efficiently transmit the excited triplet energy. However,
or negligible in aqueous solution. We ascribe the strong TTA
aggregation often greatly reduces the mobility of triplet excitons
upconversion emission in the present supramolecular assembly
and causes quenching of emission, and therefore makes strong
system to the efficient TTA process which is facilitated along the
TTA-UC emission challenging. On the other hand, the
stacked emitters through triplet energy migration and improved
supramolecular assembly may draw the energy donor and
acceptor close to facilitate the energy transfer.[6] We have
triplet-triplet energy transfer through host-guest complexation.
Introduction
The upconversion (UC) luminescence, refers to a unique
technique that converting lower photon energy excitation into
higher energy emission, have recently received growing
attention due to the potential applications in the fields such as
photocatalysis, bio-imaging, and photovoltaics.[1] Amongst
various UC mechanisms, triplet-triplet annihilation (TTA) UC, a
process whereby two triplet excited state molecules interact to
generate a singlet excited state molecule, is particularly
attractive due to the low-power, incoherent excitation, and high
upconversion efficiency.[2] In a conventional TTA-UC process,
Figure 1. Schematic illustration of the TTA-UC process. GS represents the
ground state, D and A represent the donor and acceptor respectively, the
superscript number 1 and 3 represent the singlet and triplet states respectively,
and the star represent the excited state. ISC means intersystem crossing,
TTET is triplet−triplet energy transfer and TTA means triplet−triplet annihilation.
The dark red solid arrow represents the absorption, the blue solid arrow
represents the emission and the dotted downward arrows represent
nonradiative transition.
[a] W. Xu, C. Fan, M. Rao, Dr. W. Wu, Prof. Dr. D. Su, Prof. Dr. Z.-H.
Zhong, Prof. Dr. C. Yang
Key Laboratory of Green Chemistry & Technology of Ministry of Education,
College of Chemistry, State Key Laboratory of Biotherapy, and Healthy
Food Evaluation Research Center, Sichuan University, Chengdu 610064,
China
[b] W. Liang
Institute of Environmental Sciences, Department of Chemistry, Shanxi
University, Taiyuan 030006, China
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Scheme 1 The chemical structure of the sensitizer RuCou and Synthesis route of the emitters/ annihilators A1-A3. Reagents and conditions: i) Tosyl chloride, pyridine,
r.t.; ii) NaN3, DMF/H2O, 80C; iii) triphenylphosphine, DMF, ammonia solution, r.t.; iv) Pd(PPh3)4, CsF, K2CO3, Toluene/THF, reflux; v) NaOH, Dioxane/H2O, 100C; vi) HCl,
6h.; vii) HOBT, EDC, DMF/Triethylamine
CD-based A1 and A2 showed largely improved solubility (>
5.0 mM) relative to A3 (< 0.2 mM) in pH 9.0 aqueous solution
by virtue of the excellent water-solubility of γ-CD. However,
the well-dispersed aqueous solutions of A1 and A2 showed a
Tyndall effect, and the dynamic light scattering (DLS) studies
revealed that A1 and A2 at 0.50 mM afforded nanostructures
of 190 nm and 220 nm (Figure 2a), respectively. The
supramolecular aggregations of A1 and A2 were further
confirmed by the scattering electron microscopy (SEM)
investigations, which showed long nanostrips having a width
in the range of 150-400 nm (Figure2b, c). Both A1 and A2
demonstrated TTET and TTA-UC efficiency through
supramolecular complexation in an organic solvent. In the
present paper, we report significantly improved TTA-UC in
[7]
aqueous
solution
through
supramolecular
self-
aggregation/assembly of cyclodextrin (CD)-based emitters.
Results and Discussion
Two γ-CD-based acceptors, A1 and A2, in which the 9,10-
diphenylanthracene (DPA) moiety severs as the energy
acceptor/emitter, were synthesized by reacting 6A-amino-6A-
deoxy--CD with corresponding DPA derivatives, respectively
(Scheme 1). Both the DPA-tethered -CD A1 and the DPA-
bridged -CD A2 were characterized by NMR and MS
spectroscopies.[8] CDs are widely applied molecular hosts
due to their advantages, such as water-soluble, readily
available, and capable of binding a wide range of organic
guests.[9] We have demonstrated that CDs are particularly
suitable for conducting supramolecular photochemical
reactions on account of their UV-transparent property.[10] γ-
1
exhibited sharp and distinctive H NMR signals in DMSO-d6
solution (Figure S13 and S14).[8] On the contrary, the
aromatic proton peaks of both A1 and A2 became very broad
in pure D2O (Figure S13-15), [8] indicative of a water-induced
aggregation of the emitters. This is confirmed by the fact that
increasing the D2O content in CD3OD led to a gradual upfield
shift of the aromatic proton peaks (Figure S15). This result
also suggested that -stacking plays an important role in
the aggregation of A1 and A2 in the aqueous solution.
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60
a)
50
A1, 190nm
40
A2, 220nm
30
20
10
0
1
1000
10 Size c1la0s0ses / nm
2.0
1.0
[A1]
1.0 mM
H O
2
20% MeOH / H O
d)
e)
6
4
f)
[A2]
1.0
0.5
2
1.0 mM
0.01 mM
50% MeOH / H O
2
70% MeOH / H O
0.01 mM
2
2
MeOH
0
0.0
0.0
-2
-4
-0.5
-1.0
225
250
275
300
240
280
320
250
300
350
400
Wavelength / nm
Wavelength / nm
Wavelength / nm
Figure 2. (a) DLS of A1 (black, 0.1mM) and A2 (red, 0.1mM) in H2O; (b, c) SEM images of nanostructures formed by 0.10 mM (b) A1 and (c) A2 in H2O, and
concentration-dependent CD spectra of (c) A1 and (d) A2 respectively, from 1.0 × 10-5 M to 1.0 × 10-3 M, in the H2O at 25 ℃. (f) CD measurement spectrum of A2
in different proportions of methanol aqueous solution, [A2] = 0.1 mM at 25 ℃.
The DPA-tethered
positive induced circular dichroism signal peaked at the
1Bb transition (258 nm) of DPA even at
low

-CD A1 afforded an obvious
intensive blue fluorescence band at ca. 430 nm in
aqueous solution (Figure 4a), giving emission quantum
yields of 82% and 90%, respectively (Table 1), which is
apparently higher than that of A3 (69%). Increasing the
concentration of emitters did not significantly change the
a
concentration of 0.01 mM (Fig 2d). Increasing the
concentration did not lead to significant change of the
dissymmetry factor (g value), implying the formation of
aggregates at very low concentration. According to the
sector rule proposed by Kajitar et al, the positive induced
circular dichroism observed for 1Bb transition should arise
from the inclusion of the anthracene moiety of DPA in the
fluorescence spectra of emitters. At
a
diluted
concentration, A2 presented a lifetime of 5.19 ns.
However, a new component having a longer decay time
(33.08 ns) appeared and increased with the
concentration of A2 (Figure S16),[8] presumably due to
the protection from solvent collision by forming
aggregates.
cavity of
of A1 is partially self-included and partially inserts into
the CD cavity of another A1 so as to form
γ
-CD.[11] We propose that the anthracene moiety
a
supramolecular polymer (Figure 3). On the contrary, A2
showed weak circular dichroism signal at low
concentration, and a positive exciton-coupling type
circular dichroism gradually grew up with the
concentration of A2 (Figure 2e). The exciton-coupling
type circular dichroism signal vanished when adding
methanol to the aqueous solution of A2 (Figure 2f),
demonstrating the important role of hydrophobic
complexation in the formation of aggregation. This
observation combined with the large NMR upfield shift
Table 1. Photophysical related parameters of the emitters and the
sensitizer and upconversion quantum yield.a
abs
/nm
 / (M-1
em
/nm
PL
/nsf
UC
cm-1)c
/%d
/%g
3.70
6.87
--
A1
A2
375
375
375
475
7591
7976
430
435
435
585
82
6.20
5.19
90
A3
RuCoub
6339
63300e
69
8.4e
5.62
10511
--
[a] In water at 1  10-5 M. [b] In deaerated water. [c] Molar absorption
coefficient at the absorption maxima. [d] Luminescent quantum yields
using the prompt fluorescence of DPA as the standard (Ф = 0.90, in
Cyclohexane). [e] Literature data,[3f] [f] Luminescent lifetimes. [g]
upconversion quantum yields in deaerated water with the prompt
phosphorescence of RuCou (8.4% in MeCN) as the standard.[3f]
accompanying with the aggregation validated a
-
stacking of DPA moiety with a right-handed helicity
(Figure 3).[12]
All three emitters A1
-A3 exhibited the character
absorption of central DPA unit. A1 and A2 emitted
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Figure 3. Schematic representation of the self-aggregation of A1 and A2 in aqueous solution.
1.2
Emission
Abs
0.6
0.4
0.2
0.0
A1
A2
A3
A1
A2
A3
RuCou
1.0
RuCou 0.8
0.6
0.4

0.2
0.0
300
400
500
600
700
Wavelength / nm
1.2
1.0
0.8
0.6
0.4
0.2
0.0
10000
1000
100
10
RuCou
A2 with RuCou
A1 with RuCou
A1, A2, A3
1
0.0
5.0x103 1.0x104 1.5x104 2.0x104
400
500
600
700
800
Wavelength / nm
Time / s
Figure. 4 (a) Absorption spectra and normalized emission spectra of RuCou (10 M) and A1-A3 (10 M ) measured at room temperature in aqueous solution. (b)
Emission photography of RuCou in the absence and presence of A1/A2 photoexcited with a 473 nm laser. (c) Emission spectra of RuCou in the absence and
presence of A1/A2 at ex = 473 nm (d) UC emission decay at 445 nm of A2 with RuCou in deaerated H2O under 473 nm pulsed excitation at CA2 =0.2 mM and
CRuCou = 10 M
RuCou showed an absorption maximum at 475 nm with a
the emitters A1-A3 was studied in deaerated aqueous
solution by using a 473 nm solid-state laser as a light source
with RuCou serving as a sensitizer. RuCou itself emitted
high molar coefficient of 63300 M-1 cm-1 in CH3CN, which is
significantly higher than that of tris(2,2’-bipyridine) ruthenium
[3f]
(II) due to the existence of the coumarin unit,
TTA-UC of
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5x106
emission could be observed when using A3 as the emitter
(Figure S20). Photoexcitation at 473 nm in the absence of
RuCou resulted in completely no fluorescent emission for all
emitters A1-A3. The emission spectra sensitized with RuCou
were well identical to the fluorescent spectra obtained by
direct photoexcitation at ex = 400 nm, and displayed decays
in microsecond time scale (Figure 4d), which further
supported the TTA-UC-based mechanism
On the contrary, A1 and A2 showed only weak TTA-UC
emission upon sensitization with RuCou in DMSO in which
both A1 and A2 was well soluble (Figure 5 and Figure S21).
While for A3, much stronger TTA-UC emission was observed
in DMSO than that in H2O (Figure S22). The negligible TTA-
UC observed with A1 and A2 in DMSO could be accounted
for by the steric effect of γ-CD, which should significantly
reduce the diffusion rate of the emitters and inhibit the contact
of the central DPA unit. The sharp contrast behavior
observed with in water and DMSO, demonstrating that the
supramolecular aggregation played an important role in the
present TTA-UC system.
Em. in water
Em. in DMSO
4x106
3x106
2x106
1x106
0
400
500
600
700
800
Wavelength / nm
Figure 5. The UC emission spectra of RuCou (10 M) with A2 as the
acceptor in water (red line) and in DMSO (black line) measured at 25 C;
λex = 473 nm, PI = 6.0 mW, [A2] = 0.1 mM.
orange phosphorescence (Fig. 4b, c). Adding A1 led to a
quenching of the RuCou emission, accompanying by an
increase of a blue emission (Figure 4c).[8] An even stronger
blue emission was observed with A2, which could be clearly
viewed by naked eyes (Figure 4b), while only negligible
1.4
1.2
0.6
0.5
0.3
0.1
0.0
Laser Power
1.0
[A2]
10.4 mW
0.8
0.6
0.4
0.2
0.0
0 M
0.4 mW
200 M
400
500
600
700
800
400
500
600
700
800
Wavelength / nm
Wavelength / nm
9
6
3
0
108
Slope=1.25
107
106
Slope=2.32
100
1.0x10-4
2.0x10-4
0.0
1000
Power Density / mW·cm-2
[A2] / mol·L-1
Figure 6. (a) Power-dependent UC emission of A2 with RuCou in deaerated H2O at CA2= 0.2 mM and CRuCou = 10 M. Inset: Double logarithmic plot of the UC
emission intensity as a function of light power density. (b) Phosphorescence of RuCou as a function of A2 concentration in deaerated H2O at 25 °C (ex = 473 nm,
PI = 6.0 mW, CRuCou = 2.0 M). The inset shows the Stern-Volmer plot. (c) CD spectra of A2 at different concentration of RuCou in the H2O at 25 °C, CA2 = 0.4
mM. (d) TTA-UC spectra of A2 as a function of the concentration of 1-amantadinemethylamine measured in deaerated H2O at 25 °C. ex =473 nm, PI = 6.0 mW,
CA2 = 20 μM, CRuCou = 15 μM.
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20
10
0
a)
b)
[A2]
0
0.3
[RuCou]
200M
15 M
0.2
0.1
0.0
0 M
-10
-20
350
400
450
500
250 300 350 400 450 500
Wavelength / nm
Wavelength / nm
Figure 7. a) UV-vis measurement of RuCou with different concentration of A2 in the H2O. [RuCou] =20 μM; b) CD spectra of A2 at different concentration of
RuCou in the H2O at 25 °C, CA2 = 0.4 mM.
On the other hand, the phosphorescence of RuCou is
quenched by increasing the concentration of emitters. The
phosphorescence quenching analyzed by the Stern-Volmer
equation represented nearly linear relationship (Fig 6d and
Figure S24).[8] The observed quenching constants kobs were
derived on the basis of Stern-Volmer plots, to give 4.16 × 109
M-1·s -1 and 3.93 × 109 M-1·s -1 for A1 and A2, respectively.
These kobs values are close to the diffusion rate constant of a
small molecule in water (kdiff = 7.4 × 109 M−1 s−1).[16] Since A1
and A2 form aggregates in aqueous solution, the effective
concentration should be much smaller than their molar
concentration added into the solution. Therefore, the kobs
values are unexpectedly high and further indicated a highly
efficient triplet energy transfer from RuCou to the emitters.
The coumarin unit of RuCou is an idea guest that has a
moderate association constant with CD.[9a] ITC study
indicated that RuCou complexed with native γ-CD with a
relatively strong association constant of 2750 M-1 at 25 C in
water (Figure S18). The complexation of A1 and A2 with
RuCou was demonstrated by the UV-vis and circular
dichroism spectral investigation (Figure 7). For the
complexation with A2 as an example, adding A2 to the
solution of RuCou led to a decrease and bathochromic shift
of the MLCT band of RuCou, at where A2 has no absorption
(Fig 7a). Moreover, keeping the concentration of A2 at 0.4
mM and gradually increasing the concentration of RuCou
caused a decrease of the exciton coupling circular dichroism
of the 1Bb band and a growth of a shoulder at 295 nm,
implying a change of stacking geometry of A2 due to the
complexation of RuCou (Figure7b). A new induced circular
dichroism signal was observed at the MLCT band of RuCou,
further demonstrating the binding of RuCou by CD cavity.
We therefore ascribed the highly efficient TTET to the
complexation of RuCou with γ-CD, which is consistent to our
To get insight into the mechanism underlying the strong
TTA-UC of the supramolecular assembly in aqueous solution,
we recorded the TTA-UC emission of A1 and A2 as a
function of excitation power density. The UC emission
increase with the excitation power (Figure 6 and Figure S23),
and the double logarithmic plots of the UC intensity vs light
power density showed two different regimes, both fit well with
linear regressions. For the TTA-UC of A2 as an example (Fig
6b), it followed a quadratic process (slope = 2.32) until the
power density was increased to 195 mW /cm2 and then
switched to the linear process (slope = 1.25) with the laser
power. This observation demonstrated that the TTA became
the dominant decay pathway for the A2 triplet at 195 mW /cm-
2. A threshold value of 586 mW /cm2 was observed with A1,
which is much higher than that of A2, implying that the TTA
process is more efficient for A2 than for A1.
Based on the correlation between the diffusion rate
constant and the threshold value (eq. 2),[13, 4a] the diffusion
rate constant for the aggregates of A2 was estimated to be
4.210-4 cm2 s-1, which is significantly higher than that of DPA
(1.210-5 cm2 s-1)[13] in low viscosity solvent. This is slightly
unexpected since it revealed a triplet energy transfer faster
than the molecular diffusion. For conventional TTA-UC, the
energy transfer is realized through molecular collision which
is basically diffusion-limited, because both the TTET and TTA
processes follow the Dexter mechanism.[14] The above results
indicated that the triplet energy transfer underwent through a
more efficient pathway other than molecular collision. We
attributed the highly efficient triplet energy transfer to the
energy migration in the aggregation,[4,15] which allows for
faster and efficient exciton transport of a triplet excited DPA
along the aggregation.
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previous observation in supramolecular TTA-UC systems.[7]
Under optimized concentration and laser power condition, A1
and A2 offered high upconversion quantum yield of Φuc=
6.87% and 3.70% (table 1), respectively. The overall
upconversion capability[3g] (= UC, where  is the molar
extinction coefficient of the triplet sensitizer and UC is the
upconversion quantum yield) of the assemblies are
significant considering the large of the sensitizer at the
excitation wavelength. Previously, the largest quantum yield
of 13% (table S1) in water was reported but with much
smaller at the excitation wavelength. [4a, 17]
Gradually increasing the concentration of 1-adamantane
methylamine to the aqueous solution containing A2 and
RuCou led to a decrease of TTA-UC intensity (Figure 8). This
could be reasonably accounted for by the competitive
complexation of 1-adamantane methylamine that inhibits the
complexation of RuCou. This further demonstrated the
significance of the supramolecular complexation of RuCou in
this TTA-UC system and points to a new potential application
of the TTA-UC-based supramolecular system for sensing
organic guests in aqueous solution.
Experimental Section
General Materials and Methods
All the reagents and solvents for synthesis and measurement
were commercially available and was used as received
unless specified otherwise. All aqueous solutions were
prepared with deionized water. 1H NMR spectra were
recorded at room temperature on Bruker AMX–400 (operating
at 400 MHz for 1H NMR and 100 MHz for 13C NMR) in D2O or
d6-DMSO with TMS as internal standard. HRMS were
measured in a waters–Q–TOF Premiers (ESI). UV-vis spectra
and UV–vis titration were obtained on JASCO v–650.
Fluorescence spectra and Fluorescence lifetime decays were
acquired by using fluoromax–4 spectrofluoremeter. The
circular dichroism spectra were taken on JASCO J–1500, and
the DLS were detected by Zetasizer Nano ZS90. The
inclusion constant of RuCou and native γ-CD is measured by
GE MicroCal VP-ITC. All samples in upconversion
experiments were deaerated with argon for ca. 15 min before
measurement and the gas flow is kept during the
measurement.
0.8
TTA Upconversion Measurement: Diode pumped solid
state (DPSS) laser (473 nm) was used as the light source for
the upconversion measurement and the diameter of the laser
spot is ca. 1 mm. The upconversion quantum yields (uc)
were determined with the prompt fluorescence of RuCou (the
structure is shown in scheme 1 ( = 8.4 % in CH3CN) as the
standard. The upconversion quantum yields were calculated
with eq. 1, where uc stands the upconversion quantum
yields, A, I and  represents the absorbance, integrated
photoluminescence intensity and the refractive index of the
solvent, sam represents the sample, and std represents
standard (eq. 1). The equation is multiplied by factor 2 in
order to make the maximum quantum yield to be unity. [3c]
[1-Ada]
0 M
0.6
80 M
0.4
0.2
0.0
400
500
600
700
800
Wavelength / nm
Figure 8. TTA-UC spectra of A2 as a function of the concentration of 1-
amantadinemethylamine measured in deaerated H2O at 25 °C. ex =473
nm, PI = 6.0 mW, CA2 = 20 μM, CRuCou = 15 μM.
2
)
Φ푈퐶 = 2Φ푠푡푑 ∗ ( 퐴푠푡푑 ) ∗ (퐼퐼푠푎푚) ∗ (휂휂푠푎푚
(eq.1)
퐴푠푎푚
푠푡푑
푠푡푑
The TTET efficiency was evaluated by the Stern-Volmer
quenching constants, with increasing acceptors A1 or A2
concentration in the solution, the concentration of the
Conclusions
sensitizer was fixed at 2.0  10-5
M
In summary, we demonstrated that supramolecular assembly
in aqueous solution can significantly improve the TTA-UC
efficiency through enhancing TTET from sensitizer to emitter
through host-guest complexation and facilitating TTA process
along stacked emitters through triplet energy migration. Up to
Φuc= 6.87% was obtained in pure water with the emitter
bridged γ-CD derivatives. Competitive complexation with the
sensitizer leads to quenching of TTA-UC emission. The
present system not only demonstrates the significance of
supramolecular assembly in achieving highly efficient TTA-
UC in aqueous solution but also opens a new window for the
application of the TTA-UC-based supramolecular system in
the molecular sensing.
The triplet diffusion constant: DT (triplet diffusion constant)
of the acceptor arrays was estimated by using the following
relationship.,[13]
−2
)
−1
(
)
(
Ιth = 훼휙퐸푇8휋퐷푇푎0
휏퐴,푇
(eq.2)
where α is the absorption coefficient at the excitation
wavelength (473 nm) in cm-1, uc is the donor-to-acceptor
TTET
efficiency
(evaluated
by
the
quenching
phosphorescence intensity of RuCou at Ith), and a0 is the
annihilation distance between acceptor triplets (9.1 Å for DPA
triplets).[13] The acceptor triplet lifetime A,T was obtained by
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considering the known relationship of IUC(t) ∝ exp(-2t / A,T) ≡
exp(-t / UC).[18]
and then the solvent was removed under reduced pressure.
The residue was purified by passing through a silica plug
using DCM: petroleum ether = 1:1 as eluent to give a light
yellow solid. 530.0 mg, 1.18 mmol, yield: 13.0%. 1H NMR
(400 MHz, CDCl3) δ (ppm): 8.31 (d, J = 1.8 Hz, 2H), 8.29 (d, J
= 1.9 Hz, 2H), 7.64 – 7.61 (m, 4H), 7.59 (d, J = 1.8 Hz, 2H),
7.57 (d, J = 1.8 Hz, 2H), 7.37 – 7.34 (m, 4H), 4.03 (s, 6H).
Synthesis and characterization
Compound 1：Under N2 atmosphere, γ-cyclodextrin (10 g,
7.71 mmol) was dissolved in dry pyridine (50 mL), then, tosyl
chloride (1.60 g, 8.42 mmol) was added gradually in portions.
The reaction mixture was stirred at room temperature for 6 h,
until the amount of monosubstituted-cyclodextrin was no
longer increase (the reaction was monitored by TLC). After
completion of the reaction, the solvent was removed in
Compounds 5 and A3：To a solution of compound 4 (250 mg,
0.56 mmol) in dioxane (30 mL), was added NaOH (0.8 g, 20
mmol). The mixture was stirred vigorously and was reflux at
100C for 3 hours. Dioxane was removed by a rotary
evaporator. Then hydrochloric acid solution was added to
regulate pH to acidity. A light yellow solid was obtained
through membrane filtration. The crude product was purified
by column chromatography (silica gel, ethyl acetate/methanol
= 1:1 as the eluent), the first band was collected to give a light
o
vacuum using rotary evaporator at 80 C. Then the mixture
poured into acetone (500 mL), the precipitates collected were
dissolved in water (10 mL). This resolution-reprecipitation
process was repeated another two times to afford the crude
product as white solid. The crude product was purified by
reverse phase chromatography, using ethanol aqueous
solution by gradient elution from 0-30% to afford the target
product. Yield: 3.6 g, 25.8%. 1H NMR (400 MHz, D2O) δ
(ppm): 7.69 (d, J = 8.0 Hz, 1H), 7.60 (d, J = 8.0 Hz, 1H), 7.36
(d, J = 7.9 Hz, 1H), 7.17 (d, J = 7.9 Hz, 1H), 5.13-4.95 (m,
8H), 4.30 (s, 1H), 3.98-3.41 (m, 47H), 2.39 (s, 3H).
1
yellow solid 5, 92mg, Yield: 38.0%; H NMR of 5 (400 MHz,
DMSO) δ (ppm): 8.23 (t, J = 8.3 Hz, 4H), 7.63 (d, J = 7.7 Hz,
2H), 7.58 (d, J = 8.1 Hz, 2H), 7.56 – 7.51 (m, 4H), 7.48 – 7.42
(m, 4H), 3.95 (s, 3H); the second band was collected to give
1
A3 as a light yellow solid, 102 mg, Yield: 43.5%. H NMR of
A3 (400 MHz, DMSO) δ (ppm):13.21 (s, 2H), 8.23 (d, J = 7.9
Hz, 2H), 7.62 (d, J = 7.9 Hz, 2H), 7.58 – 7.53 (m, 4H), 7.49 –
7.43 (m, 4H).
Compound 2：NaN3 (0.21 g, 3.1 mmol) was added into the
solution of mono-6-tosyl-γ-CD 1 (3.5 g, 2.4 mmol) in
DMF/H2O (2.5 mL/0.5 mL), the mixture was stirred at 80C for
6 h, after completion of the reaction, the solvent was removed
under reduced pressure at 80 oC, then the crude product was
dissolved in water (50 mL) and was purified by reverse phase
chromatography, using ethanol aqueous solution by gradient
elution from 0-40 % to afford the target compound mono-6-
azide-γ-CD (2.3 g, 90.8%). 1H NMR (400 MHz, D2O) δ (ppm):
5.04 (d, J = 2.5 Hz, 8H), 3.93-3.71 (m, 32H), 3.63-3.43 (m,
16H).
Compound A1 ：A mixture of compound 5 (30 mg, 0.07
mmol), HOBT (15.1 mg, 0.11 mmol) and EDC (20 L, 0.10
mmol) was stirred in DMF (3 mL) at -15C for 3 hours.
Afterwards, the reaction was moved to room temperature,
compound 3 (100 mg, 0.08 mmol) was added, and the
reaction was continued for 24 h. The solvent was removed
under reduced pressure. The crude product was purified by
reverse phase chromatography, using 45% ethanol aqueous
solution as the eluent, Lyophilization to remove the solvent to
1
afford A1 as a fluffy solid (26.4 mg, yield: 22.1%). H NMR
Compound 3：The mixture of compound 2 (2.0 g, 1.48 mmol)
and triphenylphosphine (0.8 g, 3.04 mmol) were stirred at
room temperature for 6 h. Then, the ammonia solution (2 mL)
was added dropwise into reaction mixture, and was reacted
at room temperature for further 1 h. After the reaction, the
mixture was poured into acetone (200 mL), to afford white
precipitates, and the product was obtained after filtrating and
drying. Yield: 1.64 g, 97.4%. 1H NMR (400 MHz, D2O) δ
(ppm): 5.06 (s, 8H), 3.94-3.73 (m, 32H), 3.67-3.50 (m, 14H),
3.44 (d, J = 9.4 Hz, 1H), 3.11 (d, J = 11.9 Hz, 1H).
(400 MHz, DMSO) δ (ppm): 8.47 (s, 1H), 8.24 (d, J = 8.1 Hz,
2H), 8.10 (d, J = 8.1 Hz, 2H), 7.63 (d, J = 7.3 Hz, 2H), 7.60 –
7.50 (m, 7H), 7.45 (m, 3H), 5.95 – 5.72 (m, 16H), 5.02 (s, 1H),
4.92 – 4.88 (m, 7H), 4.63 – 4.52 (m, 7H), 3.95 (s, 3H), 3.64 –
3.32 (m, 40H). 13C NMR (600 MHz, DMSO) δ (ppm): 167.3,
166.9, 166.3, 158.8, 141.4, 136.8, 132.7, 131.9, 131.9, 131.3,
130.0, 129.3, 129.1, 129.2, 128.1, 126.7, 126.4, 126.3, 102.8,
102.1, 102.0, 84.4, 81.4, 81.1, 81.0, 73.2, 73.1, 73.1, 72.8,
72.6, 72.4, 61.5, 60.2, 52.8, 41.1.
ESI-HRMS: calcd ([C77H99NO42Na+]) m/z = 1732.5539, found
m/z = 1732.5533; calcd ([C77H99NO42K+]) m/z = 1748.5279,
found m/z = 1748.5275.
Compound 4: Under Ar atmosphere, 9,10-dibromoanthracene
(2.85 g, 8.5 mmol), 4-(methoxycarbonyl) phenylboronic acid
(3.8 g, 21.2 mmol), K2CO3 (4.2 g, 30 mmol), CsF (2.5 g, 16.4
mmol) and catalyst Pd(PPh3)4 (1.0 g, 0.86 mmol) were
dissolved in mixed solvent of dioxane/ THF/ H2O (4/6/1,
100mL) in an autoclave. The mixture was stirred at 120 C for
24 h. The reaction was quenched by adding water. DCM (100
mL) and water (50 mL) were added. The organic layer was
separated, and the aqueous layer was extracted with DCM
(3 20 mL). The combined organic layers were washed with
brine (200 mL), dried over anhydrous Na2SO4, and filtered,
Compound A2 ：A2 was obtained following a procedure
similar to that of A1, except the different dosage of reactant,
compound A3 (30.0 mg, 0.072 mmol), HOBT (30.4 mg, 0.22
mmol), EDC (40 L, 0.21 mmol), and compound 3 (300.8 mg,
0.16 mmol) was used. The crude product was purified by
reverse phase chromatography, using 20% ethanol aqueous
solution as the eluent, Lyophilization to remove the solvent to
1
afford A2 as a fluffy solid (16.4 mg, yield: 7.6%). H NMR
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10.1002/chem.201804001
Chemistry - A European Journal
FULL PAPER
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(400 MHz, DMSO) δ (ppm): 8.43 (s, 2H), 8.12 (d, J = 8.0 Hz,
4H), 7.62 – 7.53 (m, 8H), 7.45 (d, J = 9.4 Hz, 4H), 6.18 – 5.71
(m, 32H), 5.04 (d, 2H), 4.93 - 4.86 (m, 14H), 4.57 – 4.49 (m,
14H), 3.64 – 3.34 (m, 80H). 13C NMR (400 MHz, DMSO) δ
(ppm): 167.3, 141.5, 136.5, 134.2, 131.3, 129.4, 128.1, 126.3,
110.0, 102.1, 102.1, 81.4, 81.1, 81.0, 73.2, 73.0, 72.9, 72.9,
72.8, 72.7, 72.7, 72.5, 60.3. ESI-HRMS: calcd
([C112H156N2O70Na]+) m/z
2996.9691; calcd ([C112H156N2O70K]+) m/z = 3012.9436, found
m/z
3012.9435; calcd ([C112H156N2O70NaK]+), m/z
=
2996.9696, found m/z
=
=
=
3035.9334, found: m/z = 3035.9334.
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Keywords: triplet-triplet annihilation upconversion
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Wei Xu, Wenting Liang, Wanhua Wu,*
Chunying Fan, Min Rao, Dan Su, Zhihui
Zhong, and Cheng Yang*
The
diphenylanthracene-modified-
cyclodextrin derivatives
aggregates
of
9,
10-
formed
complexes with a ruthenium sensitizer in
aqueous solution, which significantly
facilitated the triplet energy transfer
among the sensitizer and emitters. The
Page No. – Page No.
Supramolecular Assembly-Improved
Triplet-Triplet Annihilation Upconver-
sion in Aqueous Solution
triplet-triplet
annihilation-based
upconverted emission in such
a
supramolecular assembly show high
emission quantum yields up to 6.9% vs
<0.5% obtained with the non-assembly
system.
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